1. Field of the Invention
The invention relates to an instrumentation for the production of fixing surfaces for a knee joint endoprosthesis on the femoral condyle that is adjacent to the knee joint and on the tibial head.
2. Background Art
A knee joint prosthesis of the type under regard is described for instance in DE 41 02 509 C2, FIG. 3 of which illustrates in particular the fixing surfaces needed for implantation of the part of the prosthesis on the femoral side, i.e. for fixing to the end of the thigh on the side of the knee. This plurality of fixing surfaces which are disposed at an angle to each other is conventionally produced by a rod, which extends in the axial direction of the bone, being inserted in the medullary space after exposure of the bones; by the aid of a saw template which is fixed to the rod and directly to the bone, the individual planes are sawed successively by means of a saw.
Positioning the templates non-displaceably during sawing requires extensive implementation, however really perfect and non-displaceable positioning will not be attained successfully. Moreover, the necessary processes are complicated, leading to comparatively high inaccuracy and unnecessarily long operation times, which places strain on the patient and ultimately also on the operating surgeon. The conventional preparation of these fixing surfaces is specified in detail for example in the leaflet entitled xe2x80x9cMC-KNIEGELENK nach Prof. Dr. Diehlxe2x80x9d, page 5 f.
It is an object of the invention to embody an instrumentation which will ensure a simple, rapid and accurate way of preparing the fixing surfaces needed for implantation of the tibial part and in particular the femoral part of a prosthesis.
According to the invention, this object is attained by a rotary milling head which is fixable in relation to the longitudinal axis of the femur and tibia, respectively, by fasteing means and which, in relation to this longitudinal axis, is angularly adjustable in a stable stop position by being pivoted, defining milling planes, and which is displaceable in the set milling plane, covering same and working as a face milling cutter or as a cylindrical milling cutter.
As a result of the design according to the invention, the fundamental problems of conventional sawing by the aid of a template no longer occur. Moreover, after treatment and fine machining (subsequent adjustment) are possible, should this be necessary or desirable.
By advantage, the fastening means comprise clamps which enclasp the respective bone.
In this case, a first clamp may grip the bone from above, the clamp having two jaws which are displaceable one in relation to the other and fixable in a stop position.
The fastening means may comprise at least a second clamp, the legs of which are approximately parallel to the longitudinal axis of the bone and displaceable one in relation to the other, with fastening thorns and/or holes into which to insert fastening screws being formed on the ends of the legs.
The thorns provided according to the invention ensure preliminary adjustment for holes to be drilled in the bone for the fastening screws or during the screwing process. The milling equipment can be detached from the fixing component at any time and later on it can be fastened again precisely in its initial position by quick-acting closures.
Preferably the milling head is designed for adjustment in height so that corresponding setting is possible for a certain fixing surface to be formed. Height adjustment may advantageously be put into practice by a threaded spindle of a stable or stabilizable stop position.
In keeping with a preferred embodiment it is provided that, with the milling angle set, the milling head is linearly translationally displayable via guide bars and movable via a pivot bearing or cross support so that a milling plane is defined in this way which can be worked successively by the milling head. The milling head has a cylindrical configuration with the surface of the cylinder forming the milling surface and the front of the cylinder running preferably parallel to the milling plane.
By advantage, further provision is made for an equipment for presetting the position of the axis of the leg, it being possible in this way to consider whether the patient has a varus-valgus deformity. Also leg rotation (varus or valgus deformity) can be corrected and adjusted accurately.
Furthermore, provision is made for equipments setting the length of a leg and the size of the prosthesis.
In the scope of the invention, it is possible to move the milling head or milling cutter manually, using the guide according to the invention.
By alterative, actuation in particular by servo motor can be provided for the setting equipments and/or the motion of the milling head in the milling plane, triggering of the servo motors being advantageously computer controlled. Correspondingly, it is possible to make the whole operation computer-controlled, in particular also in dependence on X-ray or computer tomography images.
For navigation purposes and in replacement of manual handling and setting of the milling head, the instrumentation may be equipped with infrared markers in order for computer-controlled setting to be possible, combined with a three dimensional computer animation on the display screen which has been obtained by a preceding computer tomography.
Details of the invention will become apparent from the ensuing description of a preferred embodiment taken in conjunction with the drawing.